TOKYO (Reuters) - The Japanese prime minister's bind over a U.S. airbase deepened on Sunday when one coalition partner said she would not agree to his plan to keep part of the base on Okinawa and another suggested the premier should quit if he can't reach a deal with Washington.
The comments by the coalition partners coincided with the latest protest against the base on the southern Japanese island, host to half the U.S. forces in Japan, and came days before an expected visit by U.S. Secretary of State Hillary Clinton.
Voter perceptions that Prime Minister Yukio Hatoyama has mishandled a feud over the Futenma airbase, along with doubts over political funding scandals, have sharply eroded the government's ratings ahead of a mid-year election the ruling Democratic Party needs to win to avoid policy paralysis.
The dispute has also frayed ties with key ally Washington.
"We cannot force Okinawa to take added burden and sacrifice," said Mizuho Fukushima, leader of the Social Democratic Party.
Asked if that meant she would not approve the government plan at a cabinet meeting, she told reporters: "That is the case."
Hatoyama's Democratic Party has a huge majority in parliament's lower house but it has relied on two tiny partners, the Social Democrats and the conservative People's New Party (PNP), to pass laws smoothly in the upper house.
A senior PNP executive said separately that Hatoyama should resign if he could not reach some agreement with Washington by his self-imposed end of May deadline. "He cannot put this off," PNP senior lawmaker Mikio Shimoji said on a TV talk show.
The Democrats and the PNP together have a bare majority in the upper house, and some conservative ruling lawmakers might be glad to see the Social Democrats depart. But a rift in the ruling bloc would be a blow ahead of an upper house election expected in July that the coalition must win to avoid policy gridlock.
Defense Minister Toshimi Kitazawa expressed concern over Fukushima's remarks but hinted they might be a political bluff.
"Each party has its basic stance but as long as she began as a member of the Hatoyama cabinet, there can be various debate but if she cannot agree, that is a problem," he told reporters.
Media quoted organizers as saying 17,000 protesters formed a "human chain" outside Futenma on a rainy Sunday, holding hands and carrying yellow balloons to symbolize their opposition to the government plan to keep some of the facility on the island.
"I strongly feel today's protest was big enough to appeal to both the Japanese and U.S. governments," Yoichi Iha, the mayor of Ginowan City, where Futenma is located, told a news conference.
Hatoyama had pledged to resolve the dispute by the end of this month but the Sankei newspaper reported on Saturday the government had abandoned the deadline and would now seek to settle the matter around November, when U.S. President Barack Obama will visit Japan for an Asia-Pacific leaders summit.
Opposition parties are demanding Hatoyama resign if he fails to meet the deadline.
"I think the prime minister's words carry great weight. He kept saying 'the end of May' and vowed to stake his job," Jiro Kawasaki, in charge of parliamentary affairs for the opposition Liberal Democrats, said on NHK television.
"If he cannot carry this out, he should take responsibility."
During the campaign that swept the Democrats to power last year, Hatoyama raised hopes Futenma could be shifted off Okinawa, despite a 2006 deal with Washington to move the facility from crowded Ginowan to a less populous site on the island.
But with the end of May looming, Hatoyama has shifted gears, saying he had come to realize some Marines must stay on the island to deter threats.
Last month, tens of thousands of Okinawans rallied to demand the premier keep his promise.
Residents of tiny Tokunoshima island also generally oppose the government proposal to shift some of Futenma's functions there. Environmentalists have criticized a plan to build a runway in pristine waters off Nago City in northern Okinawa.
U.S. officials have repeatedly said they think the 2006 agreement is the best option, while expressing willingness to talk about other plans.
(Additional reporting by Rika Otsuka; Editing by Paul Tait)